//求第n个斐波那契数
#include <stdio.h>

int Fib(int n)
{
    int a = 1;
    int b = 1;
    int c = 0;
    while(n >= 3)
    {
        c = a + b;
        a = b;
        b = c;
        n--;
    }
    return c;
}

int main()
{
    int n = 0;
    scanf("%d",&n);
    int ret = Fib(n);
    printf("%d\n",ret);
    
    return 0;
}